1. Field of the Invention
The invention relates generally to the field of communications. More particularly, the invention relates to the transmission of data over a wire communication bus.
2. Discussion of the Related Art
Radiated Electro-Magnetic Interference (EMI) is a problem inherent to most communication buses which convey data between one or more physically separated modules or computing machines. It is caused by the generation and emission of unwanted radio frequency signals that can interfere with radio receivers. In the United States, the Federal Communications Commission (FCC) has set forth strict rules about the maximum amount of EMI that a communications bus system can radiate. Equivalent regulatory bodies have similar functions in other countries.
Meanwhile, strict limits on the EMI radiated by communication bus wires in a motor vehicle have been set by the major manufacturers of motor vehicles in order to avoid objectionable interference to the receivers in entertainment, navigation, and radio communications. As data rates and the number of communications busses between modules increase, EMI compliance becomes more stringent and difficult to achieve.
A significant amount of effort has been made to reduce radiated EMI in automotive environments. EMI testing is still one of the most difficult tests for a medium to high data-rate automobile wired communication bus to pass.
Automobiles may have dedicated high-speed communications circuits to perform specific tasks. For example, a Distributed Systems Interface (DSI) bus can link safety-related sensors and components, enabling the use of intelligent sensors and actuators such as airbags, weight sensors, seatbelt pre-tensioners and side-impact protection systems.
One unsatisfactory approach, in an attempt to reduce radiated EMI in a communication bus, involves utilizing balanced or shielded wires. A disadvantage of this approach is the high-cost and added weight of such wiring. Another approach, in an attempt to solve the above mentioned problem, includes utilizing a signal shaping technique. However, signal shaping techniques can limit the maximum data rate and are limited themselves by the required data rates.
Until now, the requirements of providing a wire communication system between physically separated modules that meets EMI emission standards without reducing the data rate and signaling margins, or adding to wiring complexity and increasing the hardware cost, have not been met.